Allow me to correct an earlier error. I watched the play numerous times before, but I watched it again slowed down and it became clear that Richards wasn't off balance due to being shoved by receiver. The arm I kept seeing actually was hitting McCourty.
I still think the picture is misleading in the sense that the whiff didn't occur as it insinuated. Instead, his poor positioning made a hapless lunge the only possible outcome. Either way, it was completely on him and his error was worse than McCourty's.
Despite this change, I still think Devin deserves a significant portion of the blame... just a smaller slice than I said earlier.
EDIT: See, this is exactly what I mean.
By the time Richards took McCourty out, a tackle was already impossible. It was his own mistakes that caused Devin to miss his chance to shove Juju out of bounds.